Lean Mule Ducks
The recent introduction of mule ducks by the French breeder Grimaud Freres brings to mind the
long history of mule production in Taiwan. Admittedly the familiar White Pekin is the most
popular meat duck in the world but interest in leaner ducks should not come as a surprise. Until
now the preference of the French for leaner duck meat has been met by the Muscovy which they
call Canard de Barbarie. The Taiwanese have preferred to produce lean mule ducks to avoid the
problems involved in breeding Muscovies.

The mule ducks are the sterile progeny from a cross of two species in which common duck
females (Anas platyrynchos) are inseminated by semen from Muscovy drakes (Cairina
moschata). In Taiwan the female parent of the mule is the Kaiya, a cross of Pekin drake with
the Tsiaya, the Taiwanese egg-laying breed. This produces a market duck with extremely lean
meat; a fat content of less than 18% as compared to 30% of more fat content of purebred Pekin
ducks.

One must admit that the meat of a purebred Muscovy is just as lean as the meat of a Taiwan
mule and the Muscovy is actually more meaty. But the mules have two important advantages: first,
because there is a disparity in size between the sexes of Muscovies (female Muscovy ducklings
are only 60% as large as males at market age). This presents a problem because when the
females are heavy enough to market, the males are too large. And second, that duck mother of
the mule lays many more eggs than the Muscovy females. (After laying a clutch of eggs
muscovies become broody, unless kept in a windowless house with a carefully controlled
environment. This technique was developed in France and is, unfortunately, not feasible for
warmer countries).

Because of the low egg production of Muscovy females and the slow rate of growth of the
female ducklings meat produced by purebred Muscovies is expensive to produce. By contrast,
meat produced by the Taiwan mule duck is very competitive in cost because it exploits the best
features of each parent. The mother is an egg laying machine which will produce 250 eggs per
year under ordinary management and she is never broody. She is particularly well adapted to
artificial insemination. Male and female mules inherit the good breast fleshing of their Muscovy
father but, more to the point, female mule ducks grow as fast and as large as their brothers.
Why? Because they are genetic castrates; the mule female has no functional ovary and thus
growth is not inhibited ovarian secretions.

Moreover, mule ducklings are easy to raise. They are calm and exceptionally tame. In contrast
to the nervous, noisy Pekin, mules are completely silent. Mules swim, an important trait for
cooling in hot weather, but do not fly. Mules can be confined by a fence less than half a meter
in height.

Mule ducks take about two weeks longer to attain market weight than the Pekin but the extra cost
can be partially offset by the use of lower energy feedstuffs. Actually, their slower growth may
be an advantage; many Chinese believe that the flesh of older birds is firmer and therefor more tasty. If the shrink
in weight in cooking due to the high fat content of Pekins is considered, there
is no difference in efficiency between them and mules.

Mule ducks have been grown in Taiwan for more than 275 years. Until recently the parents
were hand mated to overcome the problem of poor fertility of eggs from natural matings of
Muscovy males and common ducks. The farmer stood in the water of the pond (two times each
week) and held the duck for the male! Nowadays artificial insemination is used, made possible
by the invention of an artificial vagina in Japan about twenty years ago.

Mule ducks are popular in other countries of Southeast Asia but they are all produced from
preincubated hatching eggs shipped to them from Taiwan. Preincubated? Eggs that hatch mules
require 32 days of incubation. Such eggs are set in incubators in Taiwan and incubated for 28
days. They are then candled to remove infertile eggs and eggs with dead embryos and packed in
plastic boxes to be shipped by air to dealers in other countries. The dealer puts the eggs on a
table and covers them with a blanket -- two days later he has duckling to sell. (Originally the
preincubated eggs were shipped by boat. The Taiwanese love to tell of the salutary effects of
the sea voyage on hatchability).

The Need for a White-feathered Mule

The French will tolerate black pinfeathers as evidence of the bird being rustic but the Chinese
demand a cleanly picked bird. Therefore the plumage of a bird must be white or the pin feathers
become more prominent and some residual black pigmentation may appear on the skin.
Producing a mule with white plumage presents an interesting problem in the genetics of plumage
color. The genes fro white in both species are recessive but they are NOT homologous, i.e.,
they are not located in the same place on the same chromosome. In this case a mating of two white
birds produces colored progeny because the genes for color previously hidden under the
recessive white will appear.

The Taiwanese have solved this problem in two distinctly different ways: 1. By breeding a
recessive white with favorable cryptomeres and 2. by ingeniously exploiting the dominant
"white runner" usually seen in Indian Runner ducks.

Breeding a Suitable Recessive White

The plumage of the indigenous egg-producing duck of Taiwan is a buff color but the Taiwanese
have never felt the need to eliminate mutant colors which appear among them. Thus a pure
breeding recessive white variety could be made in a single generation by simply selecting yellow
duckling for breeders. But as far as I know the hypostatic color genes of the recessive white bird
now in use remain to be determined.

When mated to Muscovy males his newly developed recessive white Tsiaya solved the problem
of producing mule ducklings with white plumage. But, after the introduction of the large White
Pekin ducks to the market it became apparent that a larger white mule duckling was required.
The white Tsiaya was first crossed with a White Pekin male to increase the size of the Kaiya, the
mother of the mule. Unfortunately the Pekin introduced the genes from colored plumage hidden
by his recessive plumage and many of these mule ducklings were colored instead of white.

Apparently only one private breeder succeeded in eliminating these hidden genes for color in a
recessive white Kaiya. His birds are completely white except for just a hint of buff rustiness on
the flight feathers. His method is a trade secret but I suspect this rustiness is due to lack of
hidden genes for black and that he may also have utilized the dominant gene for black as
described in the following section.

Breeding the Pied Runner Tsiaya

This ingenious solution to the problem of eliminating colored feathers in mule ducks was
developed by two Taiwanese duck breeders each working independently but with the same genetic
material (and with a little luck). They made a new pied variety of Tsiaya from the dominant
white ducks which occasionally appear among the buff Tsiaya. These ducks can be readily
identified because while mostly white they have some black feathers in the face and head. This
pattern is the expression of the incompletely dominant gene for white which is involved in the
pattern of the Indian Runner breed.

But mule ducklings from the "Runner" Tsiaya were too small so, as in the recessive white
variety, white Pekin males were crossed on Runner Tsiaya females to produce the mother of the
mule.

The Pekin Grandfather

This is where the Taiwan breeders got lucky. As we have seen, use of a white Pekin introduces
genes for color which are normally hidden by recessive white. By chance, the Pekin these
breeders used happened to also carry the dominant white runner gene so that, when crossed on
pied Tsiaya, the progeny were pied. When these pied females were mated to white Muscovy
males black down color in mule ducklings was all but eliminated.

These breeders believe that this white Pekin had originally come from Denmark. Even now
they plead with me to help find more (and bigger) white Pekins of that strain. I have not found
anyone in Denmark who knows of this special white Pekin. My duck breeder friend were just
lucky.

Of course there is more to the story than is in this outline. I shall be happy to supply more
details and references on request.